Powder metallurgy provides a cost effective way of producing components having relatively complex shapes at an acceptable cost. By compacting a powder metal into a preform and then sintering the preform into a sintered part, a porous body can be formed that is dimensionally close to the final desired component. Secondary operations, such as machining, grinding and the like can be used, and in some cases may be necessary, to bring the sintered part within dimensional specifications. The near net shape fabrication techniques used in powder metallurgy reduce the amount of time needed to complete these secondary operations and also minimize the scrap produced as the sintered parts are dimensionally very close to the final desired size of the part. However, some complex parts have dimensional requirements that make their fabrication difficult, even using powder metallurgy.
For example, a variable valve timing (VVT) rotor has many features and dimensional requirements that make fabrication difficult. The VVT rotor has a flat surface that must be extremely smooth (total tolerance of 15 microns) and that has an adjacent surface that is perpendicular to and that extends outwardly from this flat surface. During part fabrication, this flat surface can not be easily ground because of the adjacent surface. Bringing this flat surface into an acceptable range might be done in a number of ways.
Elaborate machining techniques could be used to finish this flat surface. However, these techniques are very expensive, require skilled labor, and take time to perform. Moreover, the initial compaction of a part having this kind of complex shape may require the use of high technology presses that are costly and difficult to operate and maintain.
Alternatively, a VVT rotor could be fabricated as two separate components, the flat surface ground within the specification, and then the two components could be brazed or welded together. However, even this process requires additional finishing once the parts are brazed or welded together, because thermally joining the components together induces stresses and creates distortions in the components that bring the flat surface out of the acceptable range.
Hence, there is a need for an improved method for making powder metal components having difficult to achieve dimensional requirements and a need for the powder metal components themselves.